What they should do is make his W interact more with his health, Aatrox is meant to jump between heal tanking and dealing damage, What I think they should do is change his W to something like this
Remove the 3 hit effect on them
New Effect: Whenever Aatrox takes damage 15%(lvl1),30%(lvl6),45%(lvl11),60%(lvl16) of the damage turns into Gray health,
If using Blood Thirst each AA heals him for 2%,4%,6%,8%,10% of gray health (Before including any Lifesteal he has built in)
If Using Blood price, Sacrifice 2%,4%,6%,8%,10% of gray health to deal X amount more damage
Grey health persists until out of combat for 2 seconds in which it decays
Now right of the bat this would turn him more from a fighter to a brusier however it would give the champion much more strength in general and also give players fighting as him or against him some factors to think about such as
Will I be able to survive the burst to deal the damage back?
Should I go all in or focus on wittling him down?
Should I use Blood Price for damage or Thirst for survivability?
In addition to using the gray health mechanic it could apply to his passive as well, the % his blood well is filled means the % of the grey health he has is given back to him in addition to the base heal, What this means is if Aatrox dives into their entire team he can choose to ether try to cause havoc with Blood price or try to keep their attention with Blood thirst.